VanTonderJT

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Table 4.6 Leaf area (cm2cm-2) at different growth stages as affected by K-humate

applications to three soils

As mentioned earlier an increase in the photosynthetic area especially during early growth stages resulted in higher yields. Hence, to increase the incident radiation intercepted by crops and the total biomass produced, leaf area has to be increased. This was achieved at tillering with the 6 L K-humate ha-1 split application. It is known that the leaf area increases rapidly to a maximum 17 weeks after planting, followed by a sudden decrease to half the maximum size three weeks after ear emergence. It is also known that the green mainly derive it’s carbohydrates from the ear leaves (flag leaf) and stem (Davidson, 1965). Therefore, increasing the photosynthetic area will increase a crop’s canopy and thus the leaf area index which is vital for higher biomass and yield production (Lawless et al., 2004). Haboudane et al. (2004) also stated that variables such as crop and soil factors influence leaf area index, e.g. nutrient balances and disease occurrences.

Delfine et al. (2005) found that humic acid had a marginal positive effect on growth when applied to plants grown in a relatively poor soil while plants that were adequately supplied with nutrients had a limited response to humic acid. They also suggested that a positive effect can be expected when humic acid is applied to wheat leaves in a period of water shortage and in the final stages of the crop’s growth cycle.

4.3.1.3 Tiller/ear number

Appendix 4.6 and 4.7 clearly indicated a significant difference in the number of tillers per square meter at tillering on account of soil textures, and at stem elongation on account of both soil textures and K-humate applications. At tillering and stem elongation the greatest

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number of tillers was produced by the loamy sand soil, followed by the sandy clay loam soil and then the clay loam soil. Thus, with an increase in clay content the number of tillers produced decreased. Contrasting but not significantly (Appendix 4.8) at maturity a smaller number of ears were produced by the loamy sand than the two other soils (Table 4.7).

Table 4.7 Tillering and/or ear number at different growth stages as affected by K-humate applications to three soils

Earlier mentioned, K-humate affected the number of tillers at stem elongation significantly (Appendix 4.7). The control yielded the greatest number of tillers and this was significantly more than the number of tillers obtained with the 6 L K-humate ha-1 split application.

The number of tillers increased from tillering (314 tillers m-2) to the stem elongation (359 tillers m-2), but dramatically decreased to 212 ears m-2 at maturity. This reduction is a natural occurring phenomenon in wheat. Wheat plants, depending on the cultivar, have the ability to produce numerous tillers but with resource limitations not all tillers reach maturity (Miralles & Slafer, 1999). Therefore, some tillers will either stop to develop into mature ears or will be absisiced depending on the severity of stress or resource limitations.

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4.3.2 Below-ground plant parameters

4.3.2.1 Root mass in the fertilised zone

Root mass in the fertilised zone showed no significant differences as a result of either the K-humate application by soil texture interaction or K-humate application at any of the growth stages (Appendix 4.9 – 4.11). At tillering r oot mass of the control was the greatest with the K-humate treatments showing a decrease of approximately 30% in root mass. At stem elongation and maturity the mentioned tendency was not observed.

At tillering no significant differences as a result of soil texture was observed (Appendix 4.9). Though insignificant, the loamy sand and sand clay loam soils produced greater root masses in the fertilised zone than the clay loam soil. This was not observed at stem elongation and maturity (Appendix 4.10 and 4.11). At these growth stages the mass of roots grown in the fertilised zone decreased with an increase in clay content and the loamy sand soil had a greater root mass than the clay loam soil (Table 4.7).

Table 4.8 Root mass in the fertilised zone (g m-2) at different growth stages as affected by K-humate applications to three soils

4.3.2.2 Root mass in the unfertilised zone

Similarly to root mass in the fertilised zone root mass in the unfertilised zone also did not differ on account of either the K-humate application by soil interaction or K-humate application at any of the growth stages (Appendix 4.12 – 4.14). However, soil texture

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significantly influenced root mass in the unfertilised zone at stem elongation and maturity. At both these stages the loamy sand soil produced a significantly greater root mass than the clay loam soil (S3) (Table 4.9).

In comparison, root mass in the fertilised zone was on average three times greater than in the unfertilised zone at stem elongation and maturity. At tillering the difference was smaller with root mass of the unfertilised zone half that of the fertilised zone (Tables 4.8 and 4.9).

Table 4.9 Root mass in the unfertilised zone (g m-2) at different growth stages as affected by K-humate applications to three soils

4.3.2.3 Root mass in remaining soil

Root mass in the remaining soil was not significantly affected by the K-humate application and soil texture interaction or K-humate application as a main factor. Only soil texture significantly affected root mass (Appendix 4.15 – 4 .17) at maturity. It is worth mentioning that at maturity root mass tended to be higher with K-humate application.

Interestingly, soil texture influenced root mass differently in the remaining soil than in either the fertilised or unfertilised zones. The root mass in the remainder of the sandy clay loam soil was the greatest at stem elongation and maturity (Table 4.10). This root mass

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was however only significantly different from the loamy sand soil at maturity (Appendix 4.17).

Table 4.10 Root mass in the remaining soil (g) at different growth stages as affected by K-humate applications to three soils

Trials on maize with humic acids showed significant increases in shoot and root growth (Tan & Nopamornbodi, 1979). Lulakis and Petsas (1995) also found positive results with humic acid application on tomato seedling roots. They reported that the highest number of roots were produced at concentrations of 50 to 100 ppm humic acid but an inhibitory effect was obtained when humic acid was applied at concentrations of 1000 to 2000 ppm. Vaughan and Linehan (1976) found similar results for wheat and according to Atiyeh et al. (2002) humic acids increased tomato and cucumber growth significantly. In contrast this experiment did not show a positive effect on root mass of wheat with the addition of K- humate to soil.

4.3.2.4 Root length in the fertilised zone

Root length was not significantly affected by the K-humate application and soil texture interaction, nor the main factor K-humate application (Appendix 3.18 – 3.20). However, at stem elongation a split application of 3 L K-humate increased root length with 38% compared to the control. At maturity a single application of 3 L K-humate increased root length with 33% over the control (Table 4.11).

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Root length in the fertilised zone was significantly affected at maturity by soil texture. The loamy sand soil showed a significantly greater root length (almost double) than either the sandy clay loam or clay loam soils. However, one suspects roots to develop better in sandy than more clayey soils (Pietola, 2005). At tillering root length was greatest in the sandy clay soil but at the stem elongation root length was greatest in the loamy sand soil.

Table 4.11 Root length of the fertilised zone (mm) at different growth stages as affected by K-humate applications to three soils

4.3.2.5 Root length in the unfertilised zone

Root length in the unfertilised zone was not significantly influenced by the different K- humate applications or the interaction of K-humate application and soil texture (Appendix 4.21 to 4.23). However, at tillering the greatest root length was obtained with a split application of 3 L K-humate ha-1 in the sandy clay loam soil. At stem elongation and maturity a split application of 6 L K-humate ha-1 increased root length by 25 and 29.6% respectively to the control (Table 4.12).

Root length of the unfertilised zone like that of the fertilised zone responded similar to soil texture for the same reasons (Pietola, 2005) mentioned earlier. It had to be noted that root length of the unfertilised zone was much shorter than that of the fertilised zone.

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Table 4.12 Root length in the unfertilised zone (mm) at different growth stages as affected by K-humate applications to three soils

4.3.2.6 Root length in remaining soil

The root length in the remaining soil was not significantly affected by the K-humate applications nor soil texture at any of the growth stages (Appendix 4.24 – 4.26). At tillering and stem elongation the greatest root length was obtained with a split application of 3 L K-humate ha-1, but at maturity a single application of 3 L K-humate ha-1 induced the greatest root length (Table 4.13). At the forementioned growth stages the clay loam soil produced the greatest root length followed by the sandy clay loam soil and then the loamy sand soil. However, at maturity the loamy sand soil produced the largest root length, followed by the sandy clay loam soil and then the clay loam soil.

It was reported that the incorporation of humic acids into soils stimulated root growth (Cooper et al., 1998). According to Atiyeh et al. (2002) humic acids stimulated the proliferation, branching and initiation of root hairs and could partially be attributed to enhanced nutrient uptake. The results that evolved from this experiment did not verify these researchers’ observations.

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Table 4.13 Total root length in the remaining soil (mm) at different growth stages as affected by K-humate applications to three soils

4.3.2.7 Root length index

Root length index was estimated by expressing the total root length of a pot in mm mm-2. As could be expected this index showed almost the same pattern as root mass and root length. Application of K-humate had no significant effect on root length index. The greatest root length index was once more been obtained with the split application of 3 L K-humate ha-1 at the tillering and stem elongation growth stages while at maturity a single application of 3 L K-humate yielded the greatest root length index (Table 4.14 and Appendix 4.27 - 4.29). In contrast to root mass and root length soil texture had no significant effect on root length index although that the three parameters showed similar trends.

Several studies showed that humic acid incrase root length, root number and root branching. These increases varied from single percentage digits but usually amounted to between 25 and 50% (Cooper et al., 1998). This was also supported by other researchers, but root growth inhibition was also established at high humic acids concentrations (Mylonas & McCants, 1980: Baraldi et al., 1991; Rajala & Peltonen-Sainio, 2001). In this study increases in root growth as manifested in the different parameters were mainly minute. In some instances however increases of 18% were recorded. The reason for not

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being significant could be the result of a high coefficient of variance that is typical of root studies.

Table 4.14 Root length index (mm mm-2) at different growth stages as affected by K- humate applications to three soils

4.3.3 Yield and yield components

All yield and yield components were measured at maturity.

4.3.3.1 Seed yield

Seed yield was not significantly affected by the application of K-humate (Appendix 4.30). Soil texture however significantly influenced seed yield. The loamy sand soil and sandy clay loam soil producing significantly higher yields than the clay loam soil (Table 4.14). Though insignificant, the greatest yield was obtained with a split application of 6 L K- humate ha-1 that was 3.5% more than the control. This may seem like a small percentage but it was a yield increase of 200 kg per hectare.